1. Field of the Invention
The present invention relates to a maximum power follow-up control apparatus, wherein in a dispersive power generation system including a power generator for generating DC power, such as a hydraulic power generator or a wind power generator, and a power conditioning device (hereinafter simply referred to as “power conditioner”) for converting the DC power from the power generator into AC power and for supplying the converted AC power to a system or the like, optimal power generation efficiency corresponding to output characteristics of the power generator can be obtained in the interior of the power conditioner.
2. Description of the Prior Art
Generally, various systems such as a hydraulic power generation system, a wind power generation system, a solar power generation system or a fuel engine power generation system are suggested as a dispersive power generation system.
Such a dispersive power generation system is arranged in that DC power generated in a power generator is converted into AC power in a power converter within a power conditioner and in that the AC power is supplied to loads of consumer electronics or to systems of commercial power sources.
For improving the power generation efficiency of such a dispersive power generation system, many kinds of maximum power follow-up control apparatuses have been proposed that are based on a relationship between output power of a power generator and a DC operating voltage of a power converter within the power conditioner, that is, an output voltage of the power generator, wherein the DC operating voltage is adjusted to rapidly make a power point of output power of the power generator follow up with a maximum power point.
FIG. 15 is an explanatory view illustrating characteristics (V-P characteristics) of DC power and DC voltage in a general solar power generator.
While characteristics will be mountain-shaped in a solar power generator as illustrated in FIG. 15, by controlling the DC operating voltage of the power converter such that the power point will reach the peak of the mountain shape, that is, the maximum power point, it is possible to maximize the power generation efficiency of the solar power generator.
However, the V-P characteristics will fluctuate depending on changes in illumination of sunlight in a solar power generator, and the maximum power point will also change in accordance with the changes in illumination.
It is therefore known for conventional maximum power follow-up control apparatuses employing a hill-climbing method (see, for instance, Japanese Patent Laid-Open Publication No. 2000-181555). FIG. 16 is an explanatory view illustrating an operation algorithm of a general hill-climbing method in a simple form.
According to the conventional maximum power follow-up control apparatus of Japanese Patent Laid-Open Publication No. 2000-181555, a DC operating voltage of a power converter is adjusted per each specified voltage V and output powers of solar batteries prior to and after adjustment are mutually compared, wherein when the output power has increased, the DC operating voltage is changed by a specified voltage V in the same direction as the previous time while it is changed by a specified voltage V in an opposite direction as the previous time for making a power point of the output power reach a maximum power point Pmax in accordance with the changes in DC operating voltages, and wherein the DC operating voltage at the time of reaching is obtained as an optimal value.
According to this maximum power follow-up control apparatus, the power point will reach a maximum power point by setting the thus obtained DC operating voltage for the power converter so that the power generation efficiency of the solar batteries can be maximized.
In this respect, such V-P characteristics also differ depending on the types of the power generator. FIG. 17 is an explanatory view illustrating V-P characteristics of a power generator of dynamic type, and FIG. 18 illustrating V-P characteristics of a hydraulic power generator from among dynamic type power generators.
In this manner, the V-P characteristics of the power generators also differ depending on the types of power generators as can be understood by comparing the V-P characteristics of the solar power generator of FIG. 15 and V-P characteristics of the power generators as illustrated in FIGS. 17 and 18.
Generally, in case of a solar power generator, the V-P characteristics are fluctuated depending on changes in illumination of the sunlight as illustrated in FIG. 19A, while in case of a dynamic type power generator, V-P characteristics are fluctuated depending on changes in dynamics (that is, changes in water volume in case of a hydraulic power generator, changes in wind power in case of a wind power generator, or changes in gas volume in case of a gas engine power generator) as illustrated in FIG. 19B.
When comparing the V-P characteristics of a solar power generator and V-P characteristics of a dynamic type power generator, it can be understood that voltage changes of maximum power points depending on changes in illumination are relatively small in case of a solar power generator as illustrated in FIG. 19A, while the voltage changes of maximum power points depending on changes in dynamics are relatively large in case of a dynamic type power generator as illustrated in FIG. 19B.
Considering a conventional maximum power follow-up control apparatus, in case of a solar power generator, a period of time for making the power point reach the maximum power point by using the hill-climbing method will not too long to badly affect the power generation efficiency although it will take some time since the voltage changes of maximum power points depending on changes in illumination are relatively small as illustrated in FIG. 19A, whereas in case of, for instance, a dynamic type power generator, it will take a long period of time until the power point is made to reach the maximum power point through a conventional hill-climbing method only in which the follow-up speed is slow since the voltage changes of maximum power points depending on changes in dynamics are relatively large as illustrated in FIG. 19B so that it is feared that the power generation efficiency during this period is badly affected.